Three-dimensional printing, also known as additive manufacturing, is a process of making a three-dimensional solid object from a digital model of virtually any shape. Many three-dimensional printing technologies use an additive process in which an additive manufacturing device forms successive layers of the part on top of previously deposited layers. Some of these technologies use extruders that soften or melt extrusion material, such as ABS plastic, into thermoplastic material and then emit the thermoplastic material in a predetermined pattern. The printer typically operates the extruder to form successive layers of the thermoplastic material that form a three-dimensional printed object with a variety of shapes and structures. After each layer of the three-dimensional printed object is formed, the thermoplastic material cools and hardens to bond the layer to an underlying layer of the three-dimensional printed object. This additive manufacturing method is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
Many existing three-dimensional printers use a single extruder that extrudes material through a single nozzle. The printhead moves in a predetermined path to emit the build material onto selected locations of a support member or previously deposited layers of the three-dimensional printed object based on model data for the three-dimensional printed object. However, using a printhead with only a single nozzle to emit the build material often requires considerable time to form a three-dimensional printed object. Additionally, a printhead with a larger nozzle diameter can form three-dimensional printed object more quickly but loses the ability to emit build material in finer shapes for higher detailed objects while nozzles with narrower diameters can form finer detailed structures but require more time to build the three-dimensional object.
To address the limitations of single nozzle extruders, multi-nozzle extruders have been developed. In these multi-nozzle extruders, the nozzles are formed in a common faceplate and the materials extruded through the nozzles can come from one or more manifolds. In extruders having a single manifold, all of the nozzles extrude the same material, but the fluid path from the manifold to each nozzle can include a valve that is operated to open and close the nozzles selectively. This ability enables the shape of the swath of thermoplastic material extruder from the nozzles to be varied by changing the number of nozzles extruding material and which ones are extruding material. In extruders having different manifolds, each nozzle can extrude a different material with the fluid path from one of the manifolds to its corresponding nozzle including a valve that can be operated to open and close the nozzle selectively. This ability enables the composition of the material in a swath to vary as well as the shape of the swath of thermoplastic material extruder from the nozzles to be varied. Again, these variations are achieved by changing the number of nozzles extruding material and which ones are extruding material. These multi-nozzle extruders enable different materials to be extruded from different nozzles and used to form an object without having to coordinate the movement of different extruder bodies. These different materials can enhance the ability of the additive manufacturing system to produce objects with different colors, physical properties, and configurations. Additionally, by changing the number of nozzles extruding material, the size of the swaths produced can be altered to provide narrow swaths in areas where precise feature formation is required, such as object edges, and to provide broader swaths to quickly form areas of an object, such as its interior regions.
In these multi-nozzle extruders having their nozzles in a common faceplate, the movement of the faceplate with reference to the build platform as well as the orientation of the faceplate with respect to the XY axes of the platform are critical to the formation of a swath. As used in this document, a “swath” refers to the extrusion of material from any opened nozzle in a multi-nozzle extruder as an aggregate as long as at least one nozzle remains open and material is extruded from any opened nozzle. That is, even if multiple nozzles are opened, but not all of the emitted extrusions contact one another, the discrete extrusions constitute a swath. A contiguous swath is one in which all of the extrusions from multiple nozzles are in contiguous contact across the swath in a cross-process direction. At some orientations of the extruder, some of the nozzles align with one another in a way that may prevent a contiguous swath of extruded material from being formed. As shown in FIG. 7, a previously known faceplate having nine nozzles is depicted. When the faceplate is oriented as shown in the figure and moved along the 0°-180° (X) axis or the 90°-270° (Y) axis, all nine nozzles contribute to forming a contiguous swath and the swath has its greatest width. As used in this document, the term “0°-180° axis” means movement in either the 0° direction or the 180° direction with the faceplate of the extruder oriented so if all of the nozzles are open, then the widest contiguous swath that the extruder can produce is formed and the term “90°-270° axis” means movement in either the 90° or the 270° direction with the faceplate of the extruder oriented so if all of the nozzles are open, then the widest contiguous swath that the extruder can produce is formed. When the faceplate remains oriented as shown on the 0°-180° axis and 90°-270° axis, but moved in one of the directions rotated 18° from one of these axis, as shown in the far right illustration, the nine nozzles become three rows of three nozzles that are aligned with one another and the swath is only three nozzles wide with gaps between the extruded lines forming the swath. Thus, the widest swaths are produced when the faceplate of FIG. 7 is moved along the 0°, 90°, 180°, and 270° paths and the swaths are most narrow and the beads of extruded material are most separated from one another along the 18°, 108°, 198°, and 288° paths. The separation occurs because the orientation of the faceplate and the direction of the relative movement between the extruder and the platform arranges the nozzles in the faceplate into an array having orthogonal columns and rows. This arrangement reduces the distance between the lines formed by the nozzles in the columns so the lines align with one another and separates the lines by the spacing between the nozzles in a row. In the center of an object where feature differentiation is usually unimportant, the faceplate movement is preferred to be in one of the directions producing the widest contiguous swaths so object formation speed can be maximized. At the outside edges of an object where feature shapes are more varied and sometimes intricate; however, fewer nozzles, and perhaps only a single nozzle, may be opened to enable formation of the features. Unfortunately, this type of extruder operation does not capitalize on the large number of nozzles available for object formation and is inherently slow. Thus, much of the speed advantage in having multiple nozzles in a common faceplate is lost and, for many parts, more time can be spent on the outline of the object than was spent on the formation of the interior of the object. A three-dimensional object printer having multiple nozzles in a common faceplate that can exploit the number of available nozzles at the formation of object exteriors would be beneficial.